Skip to Main content Skip to Navigation
Journal articles

Technical Note : A universal method for measuring the thickness of microscopic calcite crystals, based on Bidirectional Circular Polarization

Abstract : The coccoliths are major contributors to the particulate inorganic carbon in the ocean that is a key part of the carbon cycle. The coccoliths are few microns in length and weigh few picograms. Their birefringence characteristics in polarized optical microscopy has been used to estimate their mass. This method is rapid and precise because camera sensors produce 10 excellent measurement of light. However, current method is limited because it requires a precise and replicable set up and calibration of the light in the optical apparatus. Precisely, the light intensity, the diaphragm opening, the position of the condenser, and the exposure time of the camera have to be strictly identical during the calibration and the analysis of calcite crystal. Here we present a new method that is universal in the sense that the thickness estimations are independent from a calibration but results from a simple equation. It can be used with different cameras and microscope brand. Moreover, the light 15 intensity used in the microscope does not have to be strictly and precisely controlled. This method permits to measure crystal thickness up to 1.7 µm. It is based on the use of one left circular polarizer and one right circular polarizer with a monochromatic light source using the following equation: = # $%& ,-. /0. // 1 where d is the thickness, the wavelength of the light used, the birefringence, 56 and 55 are the light intensity measured 20 with a right and a left circular polarizer. Because of the alternative and rotative motion of the quarter-wave plate of the circular polarizer, we coined the name of this method 'Bidirectional Circular Polarization' (BCP).
Complete list of metadatas

Cited literature [15 references]  Display  Hide  Download

https://hal.archives-ouvertes.fr/hal-02467596
Contributor : Luc Beaufort <>
Submitted on : Wednesday, February 5, 2020 - 10:11:21 AM
Last modification on : Tuesday, March 17, 2020 - 3:04:47 AM

File

bg-2020-28.pdf
Files produced by the author(s)

Identifiers

Citation

Luc Beaufort, Yves Gally, Baptiste Suchéras-Marx, Patrick Ferrand, Julien Duboisset. Technical Note : A universal method for measuring the thickness of microscopic calcite crystals, based on Bidirectional Circular Polarization. Biogeosciences Discussions, European Geosciences Union, In press, ⟨10.5194/bg-2020-28⟩. ⟨hal-02467596⟩

Share

Metrics

Record views

125

Files downloads

187